#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:6031)

#include <stdio.h>

int Sigma(int n)
{
	if (n == 1)
		return 1;
	return n + Sigma(n - 1);
}

int main()
{
	int n = 1;
	int result = 1;
	scanf("%d", &n);
	result = Sigma(n);
	printf("%d", result);

	return 0;
}